Outline

Objective: Trans and perimastoid surgical avenues are used in neurosurgical practice for removal of lesions localized at the brainstem. In addition, the transmastoid surgical exposures form an important component of other cranial base surgical strategies and are thus an important component of the neurosurgeon's armamentarium. The purpose of this study is to evaluate objectively the anatomic areas of the cranial base exposed by different trans and retropetrosal surgical approaches.

Methods: For our study we considered retrosigmoid approach and posterior transpetrosal approaches which we divided in retrolabyrinthine, translabyrinthine and transcochlear approaches. Each approach was performed a minimum of three times in 20 embalmed cadaveric heads. The surgical areas exposed by each approach were analytically examined by using a numerical grading system to assess the exposure of specific major anatomic and neurovascular structures. Scores were summed to evaluate the ability of a surgical approach to expose a given area.

Results: Retrolabyrinthine approach and transmastoid approaches scored highest in accessing targets localized in the most lateral aspect of the brainstem. Retrolabyrinthine approach, however, has the advantage of minimizing cerebellar retraction but both approaches offered limited control of targets anterior to the VII-VIII cranial nerve complex. Translabyrinthine approach provided adequate access to brainstem at the posterior fossa and cerebellopontine angle. However, adequate visualization of targets localized towards the clivus was difficult because of the presence of the VII-VIII cranial nerve complex. Transcochlear approach scored highest when the midline compartment was considered. This approach provided excellent access to targets localized at the brainstem along the posterior face of petrous bone and on the midline. Our study also identified sequential surgical steps in approaching and dissecting the mastoid and petrous bone.

Conclusions: Use of a numerical grading system allowed quantification of the exposure of the petroclival region afforded by each retro and transpetrosal approach, highlighting the differences among the approaches examined.